The long-term goal of this project is to develop strategies for the prevention of osteoporotic fractures in black women. Most studies have excluded black women because of the mistaken belief that osteoporosis is not a major health problem in this population. It is true that black women have a higher bone density, protective anatomic geometry of the femur, and a larger muscle mass compared to white women. Nonetheless, the incidence of hip fracture in black women is as great as 40% of that in white women. As the black population ages, osteoporosis will become even a greater health problem for this ethnic minority. Black women have lower levels of calcidiol and higher levels of parathyroid hormone (PTH) than white women. Since black women have lower indices of bone turnover, they also appear to have a relative resistance to the effect of PTH. Dietary supplementation with vitamin D3 has been shown to safely reduce bone loss and prevent hip fractures in postmenopausal white women. The strategy of vitamin D3 supplementation to prevent osteoporosis is even more cogent in black postmenopausal women compared to white women because (a) they have lower calcidiol levels, (b) they have evidence of secondary hyperparathyroidism, (c) the long-term effects and risks of hormonal replacement therapy have not been evaluated in black women, and (d) because of their higher bone mass, low risk strategies are more appropriate. There are less black women with osteoporosis at menopause, so that a modest reduction in bone loss could have a great impact on prevention of osteoporosis. The specific aim of this project is to determine if daily dietary supplementation with 800 IU (20 ug) of vitamin D3 will reduce bone loss in postmenopausal black women. A secondary aim is to evaluate the changes in the vitamin D-endocrine system and indices of bone turnover that result from long term vitamin D3 augmentation. A positive response would provide a safe, inexpensive and acceptable strategy for prevention of osteoporotic fractures in black women. If this randomized clinical trial demonstrates a positive effect on prevention of bone loss, a large scale multi-centered trial with fracture prevention as an endpoint will have merit.